Abstract

Background. Psychiatric co-morbidity is complex and ubiquitous. Our aim was to describe the extent, nature and patterning of psychiatric co-morbidity within a representative sample of the adult population of England, using latent class analysis.

Results. A four-class model provided the most parsimonious and informative explanation of the data. Most participants (81.6%) were assigned to a non-symptomatic or 'Unaffected' class. The remainder were classified into three qualitatively different symptomatic classes : 'Co-thymia' (12.4%), 'Highly Co-morbid' (5.0%) and 'Addictions' (1.0%). Classes differed in mean numbers of conditions and impairments in social functioning, and these dimensions were correlated.

Conclusions. Our findings confirm that mental disorders typically co-occur and are concentrated in a relatively small number of individuals. Conditions associated with the highest levels of disability, mortality and cost - psychosis, suicidality and personality disorders - are often co-morbid with more common conditions. This needs to be recognized when planning services and when considering aetiology.